I'm curious about which scenarios one would use a force function when using a PLC programming interface. Examples pertaining to process engineering, manufacturing, or industrial settings would be ideal.
A "force" in a PLC is the act of forcing a memory bit on or off from the PLC programming software. It is used exclusively for testing. Forcing a bit on or off over-rides all other PLC logic. You can think of it like both setting it and making it read only. "set" a bit is also an option with most PLCs and is also useful for testing. It differs from "force" in that it changes the value only once and does not over-ride any logic.
For example if I wanted to test if a light has failed, I can "force" its output bit in the PLC software to determine if it has failed or if it is an issue with the logic.
If I want to test a if some latching logic works, I would "set" the trigger and see if it responds how I expected.